CA1134938A - Remote acoustic wave sensors - Google Patents
Remote acoustic wave sensorsInfo
- Publication number
- CA1134938A CA1134938A CA000349613A CA349613A CA1134938A CA 1134938 A CA1134938 A CA 1134938A CA 000349613 A CA000349613 A CA 000349613A CA 349613 A CA349613 A CA 349613A CA 1134938 A CA1134938 A CA 1134938A
- Authority
- CA
- Canada
- Prior art keywords
- transducer
- acoustic wave
- sensor
- cavity
- housing
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/0001—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means
- G01L9/0008—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations
- G01L9/0022—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations of a piezoelectric element
- G01L9/0025—Transmitting or indicating the displacement of elastically deformable gauges by electric, electro-mechanical, magnetic or electro-magnetic means using vibrations of a piezoelectric element with acoustic surface waves
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/48—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using wave or particle radiation means
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Measuring Fluid Pressure (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
- Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Disclosed is an acoustic wave sensor, including an acoustic wave oscillator having a resonant frequency which is modulated according to changes in a physical variable and a broadcast amplifier for directly transmitting the modulated frequency as a radio frequency signal. As a surface acoustic wave pressure sensor, the sensor includes a housing defining a cavity therein, an opening in the housing communicating with the cavity, a surface acoustic wave transducer attached to the housing to close the opening and adapted to deflect in response to a pressure differential across the transducer, an amplifier coupled to the transducer in a feedback loop, the transducer thereby being adapted to modulate the resonant frequency of the loop in response to the deflection, and a broadcast amplifier for directly transmitting the modulated frequency as a radio frequency signal. As a Stoneley acoustic wave pressure sensor, the sensor includes a housing defining a cavity therein, an opening in the housing communicating with the cavity, a Stoneley acoustic wave transducer attached to the housing to close the opening and adapted to deflect in response to a dynamic pressure differential across the transducer, an orifice in the housing communicating with the cavity to equalize any static pressure differential, an amplifier coupled to the transducer in a feedback loop, the transducer thereby being adapted to modulate the resonance frequency of the loop in response to the deflection, and a broadcast amplifier for directly transmitting the modulated frequency as a radio frequency signal.
Disclosed is an acoustic wave sensor, including an acoustic wave oscillator having a resonant frequency which is modulated according to changes in a physical variable and a broadcast amplifier for directly transmitting the modulated frequency as a radio frequency signal. As a surface acoustic wave pressure sensor, the sensor includes a housing defining a cavity therein, an opening in the housing communicating with the cavity, a surface acoustic wave transducer attached to the housing to close the opening and adapted to deflect in response to a pressure differential across the transducer, an amplifier coupled to the transducer in a feedback loop, the transducer thereby being adapted to modulate the resonant frequency of the loop in response to the deflection, and a broadcast amplifier for directly transmitting the modulated frequency as a radio frequency signal. As a Stoneley acoustic wave pressure sensor, the sensor includes a housing defining a cavity therein, an opening in the housing communicating with the cavity, a Stoneley acoustic wave transducer attached to the housing to close the opening and adapted to deflect in response to a dynamic pressure differential across the transducer, an orifice in the housing communicating with the cavity to equalize any static pressure differential, an amplifier coupled to the transducer in a feedback loop, the transducer thereby being adapted to modulate the resonance frequency of the loop in response to the deflection, and a broadcast amplifier for directly transmitting the modulated frequency as a radio frequency signal.
Description
~34~
REMOTE ACOUSTIC WAVE SENSORS
Teong Lim Edward Staples BACKGROUND OF TI~E INVENTION
This invention relates to apparatus and methods for the measurement of physical variables. More particularly, the invention concerns the measurementof such variables at a remote location.
Physical variables,such as pressure, temperature, atmospheric loading, etc., are required to be measured in many different applications in research andindustrial procedures. Frequently, such variables must be measured at a remote location and information concerning the measured quantity must then be relayed to a receiving unit. In underwater communications systems utili~ing sonar, for example, remote pressure sensors are employed to detect dynamic water pressure changes which contain infQrmation useful in communications or detection systems.Such sonar pressure sensors are commonly employed on sonobuoys and in towed sensor arrays.
In the past, sensors for use in sonar and other such remote applications ~;
have employed transducers which utilize the principles of magnetostriction or -~
', .
~ 3~ !
pie70electricity to convert water pres.sure or other changes caused by a signal to changes in the amplitude of an electrical signal. I~hen the information detected by a remote pressure sensor must be relayed to another location, such an amplitude modulated signal has commonly been converted in the prior art to a frequency modulated signal and then transmitted in a radio frequency broadcastto a receiver.
Such prior art methods of detecting and relaying inform~tion concerning pressure and other physical variables are subject to a number of disadvantages.
Amplitude modulated sensors operate effectively only for relatively low frequency inputs. In addition, the output signal provided by such a sensor is at a very low level. As a consequence, the signals provided by known remote transducer designs tend to contain an excessive amount of electrical noise. Furthermore, relatively complex electronic circuitry is required in the design of such a transducer to provide the AM to FM conversion capability, with the result that prior art sensing systems have tended to be expensive, unreliable, and relatively short lived. In addition, prior art remote sensor designs have been subject to variations in output depending upon variations in the ambient temperature at the location of the sensor.
Consequently, a need has developed in the art for an improved sensing technique capable of sensing a physical variable at a remote location and relaying information concerning the variable. It would be advantageous for such a system to be highly reliable yee relatively inexpensive to construc~.
Furthermore, it would be desirable for such a system to provide a clear and distinct output signal with sufficient signal strength to be effectîvely ~ ~
transmitted to a distant receiver. -.
~a~39L~3~ 78SC4 SUMM~RY OF THE INVENTION
It is a general object of this invention to provide a new and improved technique for the measurement of a physical vari-able at a remote location.
An acoustic wave sensor, accorcling -to this invention, in cludes an acoustic wave oscillator having a resonant fre~uency which is modulated according to changes in a physical variable, and a broadcast amplifier for directly transmitting the modu-lated frequency as a radio frequency signal. The oscillator includes a Stoneley acoustic wave -transducer and an amplifier coupled to the transducer in a feedback loop, the transducer thereby being adapted to modulate the resonant frequency of -the loop.
In a preferred embodiment, the sensor is a Stoneley acoustic wave pressure sensor, which includes a housing defin-ing a cavity therein, an opening in the housing communicating with the cavity, a Stoneley acoustic wave transducer attached to the housing to close the opening and adapted to deflect in response to a dynamic pressure differential across the trans-ducer, an orifice in the housing communicating with the cavityto equalize any static pressure differential, an amplifier coupled to the transducer in a feedback loop, the transducer thereby being adapted to modulate the resonant frequency of the loop in response to the deflection, and a broadcast amplifier for directly transmitting the modulated frequency as a radio frequency signal.
The Stoneley acoustic wave transducer may include a first piezoelectric crystal having a first smooth surface, a second piezoelectric crystal having a second smooth surface contacting the first surface to define an interfa-e between the crystals, and an interdigital conductor array disposed upon the first surface and adapted to generate a Stoneley acoustic wave in the inter~ace upon the application of a radio frequency signal to the array.
A method of measuring a physical variable at a remote lo-cation, according to the present invention, includes the steps of:
B a) generating a Stoneley acoustic wave in a piezoelectric material at a known frequency, ~34938 78SC4 b) modulating the frequency of the yenerated wave in ac-cordance with a change in the physical variable, and c) broadcasting the modulated frequency as a radio fre-quency signal.
In a perferred embodiment utilizing a Stoneley acoustic wave transducer to measure pressure, the method of the inven-tion includes the steps of:
L3a~3fi~
a) coupling a Stoneley acoustic wave transducer in a feedback loop, b) mounting the transducer so that lt is deflected in response to a pressure differential, thereby modulating the resonant frequency of the feed-back loop, and c) broadcasting the modulated frequency as a radio frequency signal.
Examples of the more important features of the invention have been broadly outlined above in order to facilitate an understanding of the detailed descripeion that follows and so ehat the contributions which this invention provides to the art may be better appreciated. There are, of course, additional features of the invention, which will be described below and which are included within the subject matter of the appended claims.
BRIEF DESCRIPTION OF T~IE DRAWINGS
Additional objects, features, and advantages of the present invention will become apparent by referring to the detailed description below of the preferred embodiments in connection with the accompanying drawings, wherein like reference numerals refer to like elements throughout all the figures. In the drawings:
Figure 1 is a perspective view illustrating a typical surface acoustic wave transducer;
Figure 2 is an electrical circuit schematic for an acoustic wave oscillator circuit which may be utilized with a surface acoustic wave transducer.
Figure 3 is a block diagram illustrating an acoustic wave sensor constructed according to the present invention.
Figure 4 is a cross sectional side view of a surface acoustic wave pressure transducer.
Figure 5 is a cross sectional side view of a Stonley acoustic wave pressure transducer.
11~493~
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention utilizes an acoustic wave device to detect a physical variable. In describing the invention, it will be convenient to first refer to a particular type of acoustic wave, namely, a surface acoustic wave (known as a SAW wave). A surface acoustic wave can be made to propagate on a smooth surface of a crystalline solid. The energy content of a surface acoustic wave decays exponentially with depth into the propagating material and thus most of the wave energy is concentrated within one wave length of the surface. The surface acoustic wave, therefore, will propagate substantially independently of any conditions affecting the opposite surface of the host solid.
Now referring to Figure 1, a perspective view is provided of a typical surface acoustic wave transducer. A surface acoustic wave may be generated by an interdigital conductor array 11 of electrodes deposited on a crystalline surface at half wavelength spacings. The transmitting electrode 10 of the array includes multiple transmitting fingers 12, 14, 16, and 18.
Similarly, a receiving electrode 20 includes receiving fingers 22, 24, 26, and 28. The electrodes are deposited on a smooth surface 30 of a suitable crystalline material 32~ which typically is quartz or lithium niobate. The fingers are spaced apart by a half wavelength, the wavelength being selected so that the wave generated has a preselected frequency, taking into consideration the velocity at which a surface acoustic wave will propagate in the particular crystalline material 32 which is utilized. The amplitude and bandwidth of the generated wave are determined by the number of finger pairs employed in the array, the bandwidth being inversely proportional to the number of fingers. ~-When the device is connected to an alternating current source having the appropriate preselected frequency, its behavior is electrically equivalent to a series RLC circuit in parallel with a capacitance.
~ ,. ~ .
' ' i~3~3l~
A surface acoustic wave transducer, however, exhibits other characteristics which make it significantly more useful than its equivalent electronic circuit in certain applications. Because of these features, the surface acoustic wave transducer is especially advantageous for e~ployment as the feedback element in a crystal controlled osclllator. In this configuration, the surface acoustic wave device exhibits a much higher Q than the equivalent circuitry, on the order of 100 times the electrical circuit equivalent. Furthermore, the narrow bandwidth characteristic of the surface acoustic wave device permits a more precise frequency of resonance to be selected.
For use in this application, an amplifier is connected to the interdigital conductor array and a surface acoustic wave is generated by the transmitting electrode7 propagates on the crystalline surface to the receiver electrode, is detected,and then is supplied as an input to the amplifier. The amplifier outputis fed back to the transmitting electrode. Such an oscillator is designed so that the phase slope of the surface acoustic wave transducer is much greater than that of the other oscillator components, the transducer phase shift therebycontrolling the stability of the oscillator.
When the surface acoustic wave device is used in an oscillator in the above described manner, it is also advantageous to add reflecting barriers to reinforce the signal. As shown in Figure 1, reflecting barriers 34 are depositedon the surface of the crystalline material 32 spaced at multiples of the desiredwave length from the transmitting and receiving fingers. The barriers will reflect the propagated wave back into the array 11 for c~herent amplification of the SAW in a manner similar to laser action.
Figure 2 is a schematic illustration showing a typical circuit configuration for an oscillator employing a surface acoustic wave transducer.
The circuitry shown in Figure 2 is configured as a Pierce oscillator which is ~ ~345'~31~3 7~SC4 useful in this application because of its simplicity, due to a minimal number of components, and because it is relatively frequency stable.
One particular appliaation for the surface acoustic wave 5 oscillator configuration is as a sensor. Any stress which is introduced into the erystalline material 32 of the surfaee acoustic wave transducer will cause a change in the distance between the transmitting and receiving fingers of the array and will also change the velocity of wave propagation in the 10 crystalline material, thereby effecting a change in the reson-ant frequency of the oscillator which change will be propor-tional to the applied stress. Thus, any physical change which affects the crystal can be measured by the resulting change in resonant frequency of the attached oscillator circuitry. Be-15 cause of this frequency modulation effect, a surface acoustic wave sensor can be utilized to measure physical quantities such as temperature, pressure, atmospheric loading, particle counting, etc.
An acoustic wave sensor may be utilized for the sensing of 20 a physical variable at a remote location and for the transmis-sion of information regarding the physical variable to a dis-tant receiver. Now re~erring to Figure 3, a schematic block diagram is provided illustrating a remote acoustic wave sensor.
In Figure 3, an acoustic wave oscillator 36, including an 25 acoustic wave tran~ducer 37 and a feedback amplifier 39, ex-hibits a characteristic resonant frequency which is mod~llated according to changes in a physical variable. A broadcast amp-lifier 38 receives the modulated frequency signal from the acoustic wave oscillator 36 and amplifies the signal for trans-30 mission as a radio frequency signal. A transmitting antenna 40 receives the output o the broadcast amplifier to efficient-ly radiate the signal information to a distant receiving unit.
As discussed above, an acoustic wave sensor converts changes in a physical variable, such as pressure, to changes in a resonant 35 frequency. Since an acoustic wave oscillator may be selected to have a resonant frequency in the radio frequency range, the frequency-modulated signal from an acoustic wave sensor can be directly amplified and broadcasted. Beeause of this feature, an acoustic wave sensor o~fers significant advantages when used 40 as a remote sensor, ineluding a stronger, more noise free sig-B nal and simplified electrical circuitry, resulting in a longer life, higher reliability, and more economical costs of con-~ 3,~3~ 785C4 _ g _ struction.
An acoustic wave sensor mav be utilized to detect underwa-ter pressure changes. Illustrated in Figure 4 is a cross sec-tional side view of a surface acoustic wave pressure transducer designed for use underwater. The pressure snesor includes a housing 42 which defines a ~avity 44 therein. A surface acoustic wave transducer 46, similar to the surface acoustic wave transducer illustrated in Figure l, is attached to the housing to seal the cavity 44. In this manner, pressure changes imposed on the outer surface 4~ of the transducer 46 will cause a relative pressure differential across the trans-ducer and a resulting deflection of the transducer. The re-sulting stress will be detected by the transmitting and re-ceiving electrodes deposited on the inner surface 50 of the transducer when the electrode leads 52 and 54 are connected in an oscillator circuit as illustrated in Figure 3.
~ ow referring to Figure 5, the preferred embodiment of the invention is illustrated in a cross sectional side view of a Stoneley wave pressure transducer. The transducer of Figure 5 is similar to that of Figure 4, and also includes a housing 42 defining a cavity 44 therein. The transducer of Figure 51 however, is provided with a Stoneley wave transducer 56 which seals the cavity 44 and flexes in response to pressure differ-entials between the cavity and the environment external to the transducer. A stoneley acoustic wave is similar to a .......
` ~13~3~
surface acoustic wave but propagates at an interface between two crystalline materials, rather than on the surface of a crystalline material. The Stoneley wave transducer 56 is constructed of a first piezoelectric crystal 58 and a second piezoelectric crystal 60, which are maintained in mating contact to define an interface 62 between the crystals. Deposited on the surface of one of the crystals and positioned within the illterface 62 is an interdigital conductor array 64, which is substantially similar in structure to that of the surface acoustic wave transducer illustrated in Figure 4. As in Figure 4, the electrode leads 52 and 54 are attached to the interdigital conductor array 64 and may be connected to an oscillator circuLt as illustrated in Figure 3.
The use of the Stoneley wave device in a pressure sensor offers some significant advantages. Since the relatively fragile interdigital conductor array can be completely isolated by being placed between two crystalline materials, the Stoneley wave device is better able to withstand the effects of a harsh environment which might otherwise damage the conductor array. This feature is particularly advantageous in a corrosive environment such as salt water. In addition, a Stoneley wave aevice may be provided with an automatic adjustment feature to compensate for different ambient pressures, unlike the transducer illustrated in Figure 4. The transducer of Figure 4 must be sealed with the cavity 44 at a certain pressure, which limits the flexibility of that sensor. If the Figure 4 transducer were lowered to sufficient depths underwater,for example, the large increase in ambient water pressure around the sensor would impose a static deflection on the surface acoustic wave crystal 46, rendering it less responsive to pressure differentials. At even greater depths and higher pressures, the ambient pressure would eventually force the crystal inward until it yielded.
:: . - . , . ,, . . , -13~938 The Stoneley wave transducer of Figure 5 includes a small orifice 66 pas`sing through the side of the housing 42, so that the cavity 44 communicates with the pressure environmenc external to the transducer. The orifice 66 thus permits the pressure within the cavity 44 to equalize with the pressure outside of the transducer. The orifice, however, is sufficiently small in cross section that dynamic pressure changes over a relatively short time period, such as might be introduced by a sonar signal, still cause the transducer to deflect and generate a signal output from an attached oscillator. Because of this feature, the transducer of Figure 5 may be used at any water depth and need not be confined to a particular depth wikhin a restricted ambient pressure range.
In conclusion, although typical embodiments of the present invention have been illustrated and discussed above, numerous modifications and alternative embodiments of the apparatus and method of this invention will be apparent to those skilled in the art in view of this description. Although the invention has been described with respect to pressure sensors, for example, those skilled in the art will recognize that the principles of the invention are equally applicable to many other applications requiring the measurement of a physical variable at a remote location. Accordingly, this description is to be considered as illustrative only and is provided for the purpose of teaching those skilled in the art the manner of constructing the apparatus and performing the method of this invention. Furthermore, it should be understood that the forms of the invention depicted and descrlbed herein are to be considered as the presently preferred embodiments. Various changes may be -made in the configurations, sizes, and arrangements of the components of the invention~ as will be recognized by those skilled in the art, without departing from the scope o~ the invention. Equivalent elements, for example, might be substituted for those illustrated and described herein, parts or connections ..
``` ~ 13~93i3 might be reversed or otherwise interchanged, and certain features of the invèntion might be utilized independently of the use of other features, all as will be apparent to one skilled in the art after receiving the benefit obtained through reading the above description of the invention.
REMOTE ACOUSTIC WAVE SENSORS
Teong Lim Edward Staples BACKGROUND OF TI~E INVENTION
This invention relates to apparatus and methods for the measurement of physical variables. More particularly, the invention concerns the measurementof such variables at a remote location.
Physical variables,such as pressure, temperature, atmospheric loading, etc., are required to be measured in many different applications in research andindustrial procedures. Frequently, such variables must be measured at a remote location and information concerning the measured quantity must then be relayed to a receiving unit. In underwater communications systems utili~ing sonar, for example, remote pressure sensors are employed to detect dynamic water pressure changes which contain infQrmation useful in communications or detection systems.Such sonar pressure sensors are commonly employed on sonobuoys and in towed sensor arrays.
In the past, sensors for use in sonar and other such remote applications ~;
have employed transducers which utilize the principles of magnetostriction or -~
', .
~ 3~ !
pie70electricity to convert water pres.sure or other changes caused by a signal to changes in the amplitude of an electrical signal. I~hen the information detected by a remote pressure sensor must be relayed to another location, such an amplitude modulated signal has commonly been converted in the prior art to a frequency modulated signal and then transmitted in a radio frequency broadcastto a receiver.
Such prior art methods of detecting and relaying inform~tion concerning pressure and other physical variables are subject to a number of disadvantages.
Amplitude modulated sensors operate effectively only for relatively low frequency inputs. In addition, the output signal provided by such a sensor is at a very low level. As a consequence, the signals provided by known remote transducer designs tend to contain an excessive amount of electrical noise. Furthermore, relatively complex electronic circuitry is required in the design of such a transducer to provide the AM to FM conversion capability, with the result that prior art sensing systems have tended to be expensive, unreliable, and relatively short lived. In addition, prior art remote sensor designs have been subject to variations in output depending upon variations in the ambient temperature at the location of the sensor.
Consequently, a need has developed in the art for an improved sensing technique capable of sensing a physical variable at a remote location and relaying information concerning the variable. It would be advantageous for such a system to be highly reliable yee relatively inexpensive to construc~.
Furthermore, it would be desirable for such a system to provide a clear and distinct output signal with sufficient signal strength to be effectîvely ~ ~
transmitted to a distant receiver. -.
~a~39L~3~ 78SC4 SUMM~RY OF THE INVENTION
It is a general object of this invention to provide a new and improved technique for the measurement of a physical vari-able at a remote location.
An acoustic wave sensor, accorcling -to this invention, in cludes an acoustic wave oscillator having a resonant fre~uency which is modulated according to changes in a physical variable, and a broadcast amplifier for directly transmitting the modu-lated frequency as a radio frequency signal. The oscillator includes a Stoneley acoustic wave -transducer and an amplifier coupled to the transducer in a feedback loop, the transducer thereby being adapted to modulate the resonant frequency of -the loop.
In a preferred embodiment, the sensor is a Stoneley acoustic wave pressure sensor, which includes a housing defin-ing a cavity therein, an opening in the housing communicating with the cavity, a Stoneley acoustic wave transducer attached to the housing to close the opening and adapted to deflect in response to a dynamic pressure differential across the trans-ducer, an orifice in the housing communicating with the cavityto equalize any static pressure differential, an amplifier coupled to the transducer in a feedback loop, the transducer thereby being adapted to modulate the resonant frequency of the loop in response to the deflection, and a broadcast amplifier for directly transmitting the modulated frequency as a radio frequency signal.
The Stoneley acoustic wave transducer may include a first piezoelectric crystal having a first smooth surface, a second piezoelectric crystal having a second smooth surface contacting the first surface to define an interfa-e between the crystals, and an interdigital conductor array disposed upon the first surface and adapted to generate a Stoneley acoustic wave in the inter~ace upon the application of a radio frequency signal to the array.
A method of measuring a physical variable at a remote lo-cation, according to the present invention, includes the steps of:
B a) generating a Stoneley acoustic wave in a piezoelectric material at a known frequency, ~34938 78SC4 b) modulating the frequency of the yenerated wave in ac-cordance with a change in the physical variable, and c) broadcasting the modulated frequency as a radio fre-quency signal.
In a perferred embodiment utilizing a Stoneley acoustic wave transducer to measure pressure, the method of the inven-tion includes the steps of:
L3a~3fi~
a) coupling a Stoneley acoustic wave transducer in a feedback loop, b) mounting the transducer so that lt is deflected in response to a pressure differential, thereby modulating the resonant frequency of the feed-back loop, and c) broadcasting the modulated frequency as a radio frequency signal.
Examples of the more important features of the invention have been broadly outlined above in order to facilitate an understanding of the detailed descripeion that follows and so ehat the contributions which this invention provides to the art may be better appreciated. There are, of course, additional features of the invention, which will be described below and which are included within the subject matter of the appended claims.
BRIEF DESCRIPTION OF T~IE DRAWINGS
Additional objects, features, and advantages of the present invention will become apparent by referring to the detailed description below of the preferred embodiments in connection with the accompanying drawings, wherein like reference numerals refer to like elements throughout all the figures. In the drawings:
Figure 1 is a perspective view illustrating a typical surface acoustic wave transducer;
Figure 2 is an electrical circuit schematic for an acoustic wave oscillator circuit which may be utilized with a surface acoustic wave transducer.
Figure 3 is a block diagram illustrating an acoustic wave sensor constructed according to the present invention.
Figure 4 is a cross sectional side view of a surface acoustic wave pressure transducer.
Figure 5 is a cross sectional side view of a Stonley acoustic wave pressure transducer.
11~493~
DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention utilizes an acoustic wave device to detect a physical variable. In describing the invention, it will be convenient to first refer to a particular type of acoustic wave, namely, a surface acoustic wave (known as a SAW wave). A surface acoustic wave can be made to propagate on a smooth surface of a crystalline solid. The energy content of a surface acoustic wave decays exponentially with depth into the propagating material and thus most of the wave energy is concentrated within one wave length of the surface. The surface acoustic wave, therefore, will propagate substantially independently of any conditions affecting the opposite surface of the host solid.
Now referring to Figure 1, a perspective view is provided of a typical surface acoustic wave transducer. A surface acoustic wave may be generated by an interdigital conductor array 11 of electrodes deposited on a crystalline surface at half wavelength spacings. The transmitting electrode 10 of the array includes multiple transmitting fingers 12, 14, 16, and 18.
Similarly, a receiving electrode 20 includes receiving fingers 22, 24, 26, and 28. The electrodes are deposited on a smooth surface 30 of a suitable crystalline material 32~ which typically is quartz or lithium niobate. The fingers are spaced apart by a half wavelength, the wavelength being selected so that the wave generated has a preselected frequency, taking into consideration the velocity at which a surface acoustic wave will propagate in the particular crystalline material 32 which is utilized. The amplitude and bandwidth of the generated wave are determined by the number of finger pairs employed in the array, the bandwidth being inversely proportional to the number of fingers. ~-When the device is connected to an alternating current source having the appropriate preselected frequency, its behavior is electrically equivalent to a series RLC circuit in parallel with a capacitance.
~ ,. ~ .
' ' i~3~3l~
A surface acoustic wave transducer, however, exhibits other characteristics which make it significantly more useful than its equivalent electronic circuit in certain applications. Because of these features, the surface acoustic wave transducer is especially advantageous for e~ployment as the feedback element in a crystal controlled osclllator. In this configuration, the surface acoustic wave device exhibits a much higher Q than the equivalent circuitry, on the order of 100 times the electrical circuit equivalent. Furthermore, the narrow bandwidth characteristic of the surface acoustic wave device permits a more precise frequency of resonance to be selected.
For use in this application, an amplifier is connected to the interdigital conductor array and a surface acoustic wave is generated by the transmitting electrode7 propagates on the crystalline surface to the receiver electrode, is detected,and then is supplied as an input to the amplifier. The amplifier outputis fed back to the transmitting electrode. Such an oscillator is designed so that the phase slope of the surface acoustic wave transducer is much greater than that of the other oscillator components, the transducer phase shift therebycontrolling the stability of the oscillator.
When the surface acoustic wave device is used in an oscillator in the above described manner, it is also advantageous to add reflecting barriers to reinforce the signal. As shown in Figure 1, reflecting barriers 34 are depositedon the surface of the crystalline material 32 spaced at multiples of the desiredwave length from the transmitting and receiving fingers. The barriers will reflect the propagated wave back into the array 11 for c~herent amplification of the SAW in a manner similar to laser action.
Figure 2 is a schematic illustration showing a typical circuit configuration for an oscillator employing a surface acoustic wave transducer.
The circuitry shown in Figure 2 is configured as a Pierce oscillator which is ~ ~345'~31~3 7~SC4 useful in this application because of its simplicity, due to a minimal number of components, and because it is relatively frequency stable.
One particular appliaation for the surface acoustic wave 5 oscillator configuration is as a sensor. Any stress which is introduced into the erystalline material 32 of the surfaee acoustic wave transducer will cause a change in the distance between the transmitting and receiving fingers of the array and will also change the velocity of wave propagation in the 10 crystalline material, thereby effecting a change in the reson-ant frequency of the oscillator which change will be propor-tional to the applied stress. Thus, any physical change which affects the crystal can be measured by the resulting change in resonant frequency of the attached oscillator circuitry. Be-15 cause of this frequency modulation effect, a surface acoustic wave sensor can be utilized to measure physical quantities such as temperature, pressure, atmospheric loading, particle counting, etc.
An acoustic wave sensor may be utilized for the sensing of 20 a physical variable at a remote location and for the transmis-sion of information regarding the physical variable to a dis-tant receiver. Now re~erring to Figure 3, a schematic block diagram is provided illustrating a remote acoustic wave sensor.
In Figure 3, an acoustic wave oscillator 36, including an 25 acoustic wave tran~ducer 37 and a feedback amplifier 39, ex-hibits a characteristic resonant frequency which is mod~llated according to changes in a physical variable. A broadcast amp-lifier 38 receives the modulated frequency signal from the acoustic wave oscillator 36 and amplifies the signal for trans-30 mission as a radio frequency signal. A transmitting antenna 40 receives the output o the broadcast amplifier to efficient-ly radiate the signal information to a distant receiving unit.
As discussed above, an acoustic wave sensor converts changes in a physical variable, such as pressure, to changes in a resonant 35 frequency. Since an acoustic wave oscillator may be selected to have a resonant frequency in the radio frequency range, the frequency-modulated signal from an acoustic wave sensor can be directly amplified and broadcasted. Beeause of this feature, an acoustic wave sensor o~fers significant advantages when used 40 as a remote sensor, ineluding a stronger, more noise free sig-B nal and simplified electrical circuitry, resulting in a longer life, higher reliability, and more economical costs of con-~ 3,~3~ 785C4 _ g _ struction.
An acoustic wave sensor mav be utilized to detect underwa-ter pressure changes. Illustrated in Figure 4 is a cross sec-tional side view of a surface acoustic wave pressure transducer designed for use underwater. The pressure snesor includes a housing 42 which defines a ~avity 44 therein. A surface acoustic wave transducer 46, similar to the surface acoustic wave transducer illustrated in Figure l, is attached to the housing to seal the cavity 44. In this manner, pressure changes imposed on the outer surface 4~ of the transducer 46 will cause a relative pressure differential across the trans-ducer and a resulting deflection of the transducer. The re-sulting stress will be detected by the transmitting and re-ceiving electrodes deposited on the inner surface 50 of the transducer when the electrode leads 52 and 54 are connected in an oscillator circuit as illustrated in Figure 3.
~ ow referring to Figure 5, the preferred embodiment of the invention is illustrated in a cross sectional side view of a Stoneley wave pressure transducer. The transducer of Figure 5 is similar to that of Figure 4, and also includes a housing 42 defining a cavity 44 therein. The transducer of Figure 51 however, is provided with a Stoneley wave transducer 56 which seals the cavity 44 and flexes in response to pressure differ-entials between the cavity and the environment external to the transducer. A stoneley acoustic wave is similar to a .......
` ~13~3~
surface acoustic wave but propagates at an interface between two crystalline materials, rather than on the surface of a crystalline material. The Stoneley wave transducer 56 is constructed of a first piezoelectric crystal 58 and a second piezoelectric crystal 60, which are maintained in mating contact to define an interface 62 between the crystals. Deposited on the surface of one of the crystals and positioned within the illterface 62 is an interdigital conductor array 64, which is substantially similar in structure to that of the surface acoustic wave transducer illustrated in Figure 4. As in Figure 4, the electrode leads 52 and 54 are attached to the interdigital conductor array 64 and may be connected to an oscillator circuLt as illustrated in Figure 3.
The use of the Stoneley wave device in a pressure sensor offers some significant advantages. Since the relatively fragile interdigital conductor array can be completely isolated by being placed between two crystalline materials, the Stoneley wave device is better able to withstand the effects of a harsh environment which might otherwise damage the conductor array. This feature is particularly advantageous in a corrosive environment such as salt water. In addition, a Stoneley wave aevice may be provided with an automatic adjustment feature to compensate for different ambient pressures, unlike the transducer illustrated in Figure 4. The transducer of Figure 4 must be sealed with the cavity 44 at a certain pressure, which limits the flexibility of that sensor. If the Figure 4 transducer were lowered to sufficient depths underwater,for example, the large increase in ambient water pressure around the sensor would impose a static deflection on the surface acoustic wave crystal 46, rendering it less responsive to pressure differentials. At even greater depths and higher pressures, the ambient pressure would eventually force the crystal inward until it yielded.
:: . - . , . ,, . . , -13~938 The Stoneley wave transducer of Figure 5 includes a small orifice 66 pas`sing through the side of the housing 42, so that the cavity 44 communicates with the pressure environmenc external to the transducer. The orifice 66 thus permits the pressure within the cavity 44 to equalize with the pressure outside of the transducer. The orifice, however, is sufficiently small in cross section that dynamic pressure changes over a relatively short time period, such as might be introduced by a sonar signal, still cause the transducer to deflect and generate a signal output from an attached oscillator. Because of this feature, the transducer of Figure 5 may be used at any water depth and need not be confined to a particular depth wikhin a restricted ambient pressure range.
In conclusion, although typical embodiments of the present invention have been illustrated and discussed above, numerous modifications and alternative embodiments of the apparatus and method of this invention will be apparent to those skilled in the art in view of this description. Although the invention has been described with respect to pressure sensors, for example, those skilled in the art will recognize that the principles of the invention are equally applicable to many other applications requiring the measurement of a physical variable at a remote location. Accordingly, this description is to be considered as illustrative only and is provided for the purpose of teaching those skilled in the art the manner of constructing the apparatus and performing the method of this invention. Furthermore, it should be understood that the forms of the invention depicted and descrlbed herein are to be considered as the presently preferred embodiments. Various changes may be -made in the configurations, sizes, and arrangements of the components of the invention~ as will be recognized by those skilled in the art, without departing from the scope o~ the invention. Equivalent elements, for example, might be substituted for those illustrated and described herein, parts or connections ..
``` ~ 13~93i3 might be reversed or otherwise interchanged, and certain features of the invèntion might be utilized independently of the use of other features, all as will be apparent to one skilled in the art after receiving the benefit obtained through reading the above description of the invention.
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An acoustic wave sensor, comprising:
an acoustic wave oscillator having a resonant frequency which is modulated according to changes in a physical variable, including a Stoneley acoustic wave transducer and an amplifier coupled to said transducer in a feedback loop, the transducer thereby being adapted to modulate the resonant frequency of said loop; and a broadcast amplifier for directly transmitting said modu-lated frequency as a radio frequency signal.
an acoustic wave oscillator having a resonant frequency which is modulated according to changes in a physical variable, including a Stoneley acoustic wave transducer and an amplifier coupled to said transducer in a feedback loop, the transducer thereby being adapted to modulate the resonant frequency of said loop; and a broadcast amplifier for directly transmitting said modu-lated frequency as a radio frequency signal.
2. The sensor of Claim 1, further comprising a transmitting antenna for receiving the output of said broadcast amplifier and radiating said radio frequency signal.
3. The sensor of Claim 2, wherein said transducer further com-prises:
a first piezoelectric crystal having a first smooth sur-face;
a second piezoelectric crystal having a second smooth sur-face contacting said first surface to define an interface bet-ween said crystal; and an interdigital conductor array disposed upon said first surface and adapted to generate a Stoneley acoustic wave in said interface upon the application of a radio frequency signal to said array.
a first piezoelectric crystal having a first smooth sur-face;
a second piezoelectric crystal having a second smooth sur-face contacting said first surface to define an interface bet-ween said crystal; and an interdigital conductor array disposed upon said first surface and adapted to generate a Stoneley acoustic wave in said interface upon the application of a radio frequency signal to said array.
4. The sensor of Claim 3, wherein said sensor is adapted to detect pressure and further comprises:
a housing defining a cavity therein; and an opening in said housing communicating with said cavity, said crystals being attached to said housing to close said opening and being adapted to deflect in response to a pressure differential across said crystals.
a housing defining a cavity therein; and an opening in said housing communicating with said cavity, said crystals being attached to said housing to close said opening and being adapted to deflect in response to a pressure differential across said crystals.
5. The sensor of Claim 4, further comprising an orifice in said housing communicating with said cavity, said orifice pro-viding static pressure equalization, yet being sufficiently small that said crystals will deflect in response to a dynamic pressure differential.
6. The sensor of Claim 5, wherein said sensor is adapted to operate in an underwater environment.
7. A Stoneley acoustic wave pressure sensor, comprising:
a housing, defining a cavity therein;
an opening in said housing communicating with said cavity;
a Stoneley acoustic wave transducer attached to said housing to close said opening and adapted to deflect in res-ponse to a dynamic pressure differential across said transducer;
an orifice in said housing communicating with said cavity to equalize any static pressure differential;
an amplifier coupled to said transducer in a feedback loop, the transducer thereby being adapted to modulate the resonant frequency of the loop in response to said deflection; and a broadcast amplifier for directly transmitting said modu-lated frequency as a radio frequency signal.
a housing, defining a cavity therein;
an opening in said housing communicating with said cavity;
a Stoneley acoustic wave transducer attached to said housing to close said opening and adapted to deflect in res-ponse to a dynamic pressure differential across said transducer;
an orifice in said housing communicating with said cavity to equalize any static pressure differential;
an amplifier coupled to said transducer in a feedback loop, the transducer thereby being adapted to modulate the resonant frequency of the loop in response to said deflection; and a broadcast amplifier for directly transmitting said modu-lated frequency as a radio frequency signal.
8. A method of measuring a physical variable at a remote lo-cation, comprising the steps of:
generating a Stoneley wave in piezoelectric material at a known frequency;
modulating the frequency of the generated wave in accor-dance with a change in the physical variable; and directly broadcasting the modulated frequency as a radio frequency signal.
generating a Stoneley wave in piezoelectric material at a known frequency;
modulating the frequency of the generated wave in accor-dance with a change in the physical variable; and directly broadcasting the modulated frequency as a radio frequency signal.
9. The method of Claim 8, wherein the measured physical vari-able is pressure.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US045,506 | 1979-06-04 | ||
| US06/045,506 US4265124A (en) | 1979-06-04 | 1979-06-04 | Remote acoustic wave sensors |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1134938A true CA1134938A (en) | 1982-11-02 |
Family
ID=21938283
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000349613A Expired CA1134938A (en) | 1979-06-04 | 1980-04-11 | Remote acoustic wave sensors |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US4265124A (en) |
| JP (1) | JPS55164324A (en) |
| CA (1) | CA1134938A (en) |
| GB (1) | GB2054850B (en) |
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| FR2462695A1 (en) * | 1979-07-27 | 1981-02-13 | Thomson Csf | SENSOR USING TWO TUNABLE OSCILLATORS CONNECTED TO A FREQUENCY MIXER COMPRISING A DEVICE FOR CALIBRATING THE FREQUENCY OF THE OUTPUT SIGNAL AND METHOD OF CALIBRATING THE FREQUENCY |
| US4456013A (en) * | 1981-09-08 | 1984-06-26 | Brown University Research Foundation | Catheter |
| JPS5866843A (en) * | 1981-10-17 | 1983-04-21 | Tdk Corp | Ultrasonic image pickup method |
| JPS58144719A (en) * | 1982-02-04 | 1983-08-29 | Tdk Corp | Ultrasonic wave measuring device |
| FR2530338A1 (en) * | 1982-07-13 | 1984-01-20 | Asulab Sa | PRESSURE-SENSITIVE ELEMENT AND PRESSURE SENSOR BY APPLYING |
| US4947677A (en) * | 1988-10-05 | 1990-08-14 | The United States Of America As Represented By The United States Department Of Energy | SAW determination of surface area of thin films |
| US4994798A (en) * | 1989-08-28 | 1991-02-19 | Gte Laboratories, Inc. | Multiplexed surface acoustical wave apparatus |
| US5235235A (en) * | 1991-05-24 | 1993-08-10 | The United States Of America As Represented By The United States Department Of Energy | Multiple-frequency acoustic wave devices for chemical sensing and materials characterization in both gas and liquid phase |
| DE59205787D1 (en) * | 1992-01-03 | 1996-04-25 | Siemens Ag | PASSIVE SURFACE WAVE SENSOR THAT IS WIRELESSLY DETECTABLE |
| US5821425A (en) * | 1996-09-30 | 1998-10-13 | The United States Of America As Represented By The Secretary Of The Army | Remote sensing of structural integrity using a surface acoustic wave sensor |
| DE19724748A1 (en) * | 1997-06-12 | 1998-12-17 | Raab Karcher Energy Services G | Process for recording and evaluating temperature-dependent consumption values |
| DE29712267U1 (en) | 1997-07-11 | 1997-11-27 | Siemens AG, 80333 München | Detector body |
| DE19751214A1 (en) * | 1997-11-19 | 1999-06-10 | Raab Karcher Energy Services G | Process for recording and evaluating temperature-dependent consumption values or measured values of other physical quantities |
| GB2355801B (en) * | 1999-10-29 | 2003-07-30 | Transense Technologies Plc | Interrogation of surface acoustical wave devices |
| US6848295B2 (en) * | 2002-04-17 | 2005-02-01 | Wayne State University | Acoustic wave sensor apparatus, method and system using wide bandgap materials |
| US7043129B2 (en) * | 2000-06-16 | 2006-05-09 | Wayne State University | Wide bandgap semiconductor waveguide structures |
| US7330271B2 (en) * | 2000-11-28 | 2008-02-12 | Rosemount, Inc. | Electromagnetic resonant sensor with dielectric body and variable gap cavity |
| US7322246B2 (en) * | 2002-03-13 | 2008-01-29 | Ip Development, Llc | Pressure sensor with pressure translation |
| US6919521B2 (en) * | 2002-03-13 | 2005-07-19 | Ip Development, Llc | Pressure sensor |
| US6853075B2 (en) * | 2003-01-28 | 2005-02-08 | Wayne State University | Self-assembled nanobump array stuctures and a method to fabricate such structures |
| US20040144927A1 (en) * | 2003-01-28 | 2004-07-29 | Auner Gregory W. | Microsystems arrays for digital radiation imaging and signal processing and method for making microsystem arrays |
| US7005987B2 (en) * | 2003-10-30 | 2006-02-28 | Michelin Recherche Et Technique S.A. | Acoustic wave device with digital data transmission functionality |
| GB0329019D0 (en) * | 2003-12-15 | 2004-01-14 | Imp College Innovations Ltd | Acoustic wave devices |
| JP4511207B2 (en) * | 2004-01-29 | 2010-07-28 | 京セラ株式会社 | Pressure sensor module |
| JP4511216B2 (en) * | 2004-02-26 | 2010-07-28 | 京セラ株式会社 | Pressure sensor module |
| US7817843B2 (en) * | 2004-03-04 | 2010-10-19 | The Boeing Company | Manufacturing process or in service defects acoustic imaging using sensor array |
| US7340957B2 (en) * | 2004-07-29 | 2008-03-11 | Los Alamos National Security, Llc | Ultrasonic analyte concentration and application in flow cytometry |
| DE102004045199B4 (en) * | 2004-09-17 | 2006-08-17 | Siemens Ag | Measuring device and method for determining temperature and / or pressure and use of the measuring device |
| JP2007243918A (en) * | 2006-02-08 | 2007-09-20 | Seiko Epson Corp | Surface acoustic wave device and electronic apparatus |
| WO2007123537A1 (en) * | 2006-04-20 | 2007-11-01 | Dover Electronics, Inc. (Dba Vectron International) | Electro acoustic sensor for high pressure environments |
| US7835000B2 (en) * | 2006-11-03 | 2010-11-16 | Los Alamos National Security, Llc | System and method for measuring particles in a sample stream of a flow cytometer or the like |
| EP2156178B1 (en) * | 2007-04-02 | 2011-12-21 | Acoustic Cytometry Systems, Inc. | Methods for enhanced analysis of acoustic field focused cells and particles |
| US7837040B2 (en) | 2007-04-09 | 2010-11-23 | Los Alamos National Security, Llc | Acoustic concentration of particles in fluid flow |
| US8083068B2 (en) | 2007-04-09 | 2011-12-27 | Los Alamos National Security, Llc | Apparatus for separating particles utilizing engineered acoustic contrast capture particles |
| US7843363B2 (en) * | 2007-07-12 | 2010-11-30 | Rosemount Aerospace Inc. | Mechanical latch locking detection sensors |
| GB2451861A (en) * | 2007-08-14 | 2009-02-18 | Transense Technologies Plc | Surface acoustic wave based sensor in vented housing |
| US7661321B2 (en) | 2007-09-25 | 2010-02-16 | Rosemount Aerospace Inc. | Force sensing clevis insert |
| US8263407B2 (en) * | 2007-10-24 | 2012-09-11 | Los Alamos National Security, Llc | Method for non-contact particle manipulation and control of particle spacing along an axis |
| US8528406B2 (en) * | 2007-10-24 | 2013-09-10 | Los Alamos National Security, LLP | Method for non-contact particle manipulation and control of particle spacing along an axis |
| US8266950B2 (en) * | 2007-12-19 | 2012-09-18 | Los Alamos National Security, LLP | Particle analysis in an acoustic cytometer |
| FR2925696B1 (en) * | 2007-12-21 | 2011-05-06 | Senseor | SURFACE WAVE PASSIVE SENSOR COMPRISING AN INTEGRATED ANTENNA AND MEDICAL APPLICATIONS USING THIS TYPE OF PASSIVE SENSOR |
| US8714014B2 (en) | 2008-01-16 | 2014-05-06 | Life Technologies Corporation | System and method for acoustic focusing hardware and implementations |
| US8578783B2 (en) * | 2011-09-26 | 2013-11-12 | Rosemount Inc. | Process fluid pressure transmitter with separated sensor and sensor electronics |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3717857A (en) * | 1970-11-27 | 1973-02-20 | Athletic Swing Measurement | Athletic swing measurement system |
| US3978731A (en) * | 1974-02-25 | 1976-09-07 | United Technologies Corporation | Surface acoustic wave transducer |
-
1979
- 1979-06-04 US US06/045,506 patent/US4265124A/en not_active Expired - Lifetime
-
1980
- 1980-04-11 CA CA000349613A patent/CA1134938A/en not_active Expired
- 1980-05-08 GB GB8015203A patent/GB2054850B/en not_active Expired
- 1980-05-29 JP JP7266480A patent/JPS55164324A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| GB2054850B (en) | 1983-09-21 |
| US4265124A (en) | 1981-05-05 |
| JPS55164324A (en) | 1980-12-22 |
| GB2054850A (en) | 1981-02-18 |
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